Composite structural members such as stiffeners may be used in a variety of applications to increase the strength and/or rigidity of assemblies. For example, in the aircraft industry, structural stiffeners such as stringers may be used to strengthen a fuselage. The stringers may be contoured along their length in order to conform to curvatures in the fuselage. In some areas of the fuselage, the stringers may have compound contours along their lengths.
Composite stringers having compound contours of the type described above may be fabricated by laying up multiple plies of composite pre-preg over a tool having compound contours substantially matching those of the finished part. The layup may be formed to shape and cured using vacuum bag and autoclave processing. Fabrication techniques using pre-preg may have disadvantages in some applications. For example, in order to achieve the desired stringer contours, one or more of the pre-preg plies may require cutting, darting and/or splicing, which may add weight to the fuselage and/or cost.
Other techniques may be used to fabricate contoured stringers, such as resin infusion of dry fiber preforms. However, resin infusion may require the use of closed molds which need preparation and later cleanup after the part has been molded to shape. Moreover, alignment of the preform with resin distribution media and permeable parting films may be difficult without the use of stitching and/or tackifiers. Also, it may be difficult to control fiber angles in fiber preforms using known resin infusion techniques. Variations in fiber angles may result in undesired performance characteristics in the finished part.
Accordingly, there is a need for a method and apparatus for fabricating composite structural members having compound contours that reduce tool handling and which facilitate alignment of composite charges to better match tool contours. There is also a need for a method and apparatus as described above which may substantially eliminate the need for clean up of tooling following part molding, and which may be adapted for resin infusion processing using open molds.